(1) Field of the Invention
This invention relates generally to means for retrieving cable arrays which are towed on the surface of the ocean, and particularly, to a grapnel having rollers and ramps which enable a towed cable array to be retrieved without damaging the array.
(2) Description of the Prior Art
For the simulation of submarines during antisubmarine warfare exercises, naval personnel employ the use of cable arrays containing hydrophones, acoustic projectors, etc. These cable arrays are attached to and towed behind a torpedo-like vessel. When the exercise is completed, the vessel and array must be retrieved. In this regard, there are several existing devices which are used to retrieve marine targets, weapons, cable arrays, vessels, etc., floating on the ocean surface. One such device is disclosed in U.S. Pat. No. 5,494,240. This device enables a floating marine target to be retrieved by personnel in a helicopter hovering above the target. After the target is retrieved, the array must also be retrieved. Conventionally, simple grapnels having two U-shaped metal hooks positioned perpendicularly to each other and attached to a center stock are used to retrieve towed arrays. The array is retrieved by placing one of the metal hooks under the array and hoisting the array up to the helicopter. Although this type of grapnel is effective for retrieving arrays, it can develop sharp edges on the hooks, which can cause serious damage to the towed array. It can also cause high loads on the array, due to the friction as the array passes over the metal hook in a tight band, which can damage the array jacket and internal wires when it passes over the hook or where the array attaches to the target. The high loads also cause difficulty and fatigue to the grapnel operator.
Another type of grapnel used has two rollers positioned on either side of a center plate. In use, pairs of the grapnel are placed under the array and hoisted to the helicopter. The rollers reduce damage to the array by reducing the potential engagement with sharp edges associated with the above-described grapnel. Furthermore, since the array is allowed to shift on the grapnel with the aid of the rollers, damage is less likely to occur during its retrieval. However, this type of grapnel also has disadvantages in that it is 2-3 times heavier than the simple grapnel described above, and because the grapnel has only two pairs of rollers for capturing the array, the rollers being on opposite sides of the center plate, retrieval of the arrays is time consuming because twisting of the grapnel due to hydroplaning can make it difficult to line up the rollers with the array in order to capture it. Accordingly, there is a perceived need for an improved grapnel.